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Spark Plug Torque

pnguzzi

pnguzzi

Cruisin' Guzzisti
Joined
Sep 8, 2009
Messages
144
Had an interesting experience. On a ride, thought I blew a head gasket, turns out that the NGK spark plug snapped at the top of the threads blowing the porcelain isolator and plug out :twisted: .
Fear set in, how the hell do we get that out. Let the shop handle it.. spun right out.

Point of this post: Chatting with NGK, they do not recommend any lubricant/anti-seize on the plugs since it leads to over torqueing. The tech noted that their plugs already have a coating on them. Furthermore the manuals spec. of 11 ft*lbs is to high it should be 7 to 8 ft*lbs.
 
https://www.guzzitech.com/component/jmrphpbb/160/7136.html?p=69860#p69860

scottmastrocinque said:
Brian UK said:
We recently had a case of a spark plug shearing off on a Stelvio. The bits were retrieved and sent to NGK (UK)
http://motoguzziclub.co.uk/forum/forum_posts.asp?TID=12011 (You have to be registered to see it).
Response was that it had been over torqued, they (NGK) recommend 8 - 10 Nm. plus 1/3 turn on a new plug, or 1/12 turn on an old one. Guzzi seem to recommend anything between 20 and 30Nm.
Click to expand...

I just experienced the same thing today. I should learn to trust myself better. When I did the initial service, I used the Stelvio Torque Guide which I got from the downloads section. The value it has for spark-plug torque is 30 Nm or about 22ft/lb. This seemed way high to me but I didn't listen to that little voice in the back of my head.

Well, why riding, my bike started kicking and running like crud. Got home, and tossed her on the lift. After some investigation, I decided to "sniff" around the motor, literally for a leak someplace. Upon getting my head down by the side-relief cut into the cylinder, I smelled both unburnt fuel and the nasty smell of burnt fuel/chemicals. Hmm.

Took off spark plug cover, and went to remove spark plug which came out in about 2 secs. What the Hell!!!

GuzziBrokenSparkPlug003_640x480.jpg


GuzziBrokenSparkPlug002_640x480.jpg


The threads were still in the head when I lifted out the plug with it's naked insulator! Luckily, I was able to use an extractor and a long thin socket bar to twist out the broken thread. Luckily nothing broke off and fell into the engine.

Of course, tomorrow is Sunday, and I have a snowball's chance in hell of finding this unique plug here in Northwest Ohio. lol.

Word to the wise, use NGK's torque specs sheet. The Guzzi torque sheet is WRONG WRONG WRONG at least in this case! Could have been disastrous!

476_695x900.jpg
Click to expand...
 
Yup.....almost got bit by the 22 ft-lb also.

I tighten to 12 NM : ~8ft lbs and have not had any problems.

Interesting point about the anti seize. I have always put it on but perhaps I am still old school.....

Did some reading at NGK's site and found the following document.

Learn something new everyday.
 

Attachments

  • tb-0630111antisieze.pdf
    191.5 KB · Views: 94
When torque values are that low I go by feel. All you need is just enough to crush the gasket. Any more is redundant.
 
Info in Guzzi manuals is the best example I know of a possible quantum effect visible at the macroscopic level - it's inherently unstable.
 
I noted in the Griso manual that the plug spec is with 'Molycote' which I assume is the thread lubricant of the same name. Ignore that and go with the 8 ft-lb read here?
 
The safest way is to use the supplied plug wrench and trust your own strength to change plugs. Lot less brutal than a torque wrench.
 
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